An accessory device, as for example an audio device like a headphone, a hands free set or a speaker system, may for example comprise a passive device, for example a microphone. The accessory device may also contain an active device, for example an active audio device. The active audio device may for example contain an active noise compensation, ANC, device or an active audio speaker device. Such active devices are commonly powered for example by means of batteries in the accessory device.
On the other hand, the accessory device is commonly connected to a host device, for example a mobile phone, a smartphone, a tablet computer, a personal computer, a television or the like. For example in case the accessory device is an audio device, the connection may be implemented via a standard audio cable, for example a standard 4-pole or 3-pole audio cable for example with 3.5 mm jacks. The host device commonly contains a battery or an external power supply.